I think its a good idea... I've thought about this one myself. I think it would be easy to add in, as long as you didn't over-complicate it with a hundred "what ifs" ... I think if you simply had it so that if a horse is killed first, then the rider is thrown and suffers some sort of health loss. If the rider is killed first then just simply have the horse run around losing health until it dies. (maybe it could cause injury to units it comes into contact with) I think doing it that was adds that slight bit more realism without over complicating, having the horse die removes worrying about having other units mount it etc, but adds to the game by creating a real, unpredictable atmosphere to battles. It would be frustrating having some of your own units trampled by a horse going mad, but may make u think more tactically about where you send cavalry. Also I like the idea of the horse automatically losing health and dieing because then you wont end up with a stack of horses running around - which would be pointless. Okay I just wrote way too much for that =P
